By Stacy Reed
25-Apr-2006
To anyone just starting out, the huge list of image file types can seem a bit daunting. Understanding the differences in file formats is vital to printing, storing, and sharing your images online. This is a series in which we'll explore image file types, compression, resolution, printing tips, and other interesting things you might not have known about digital imaging. In today's article, I'll address the differences between raster and vector images and show you some software that can help make digital imaging fun for all ages.
Raster (bitmap) images are comprised of pixels. When the computer saves a raster image, in essence, it applies a grid to the image and assigns data to all of the squares in the grid based on their color and location. These squares are called pixels. On the other hand, vector image data is recorded mathematically in terms of geometric shapes, points and lines called primitives. Generally, you will find that vector image files are smaller because they only have to store all those coordinates whereas raster images need to record data for every pixel. However, you'll probably find yourself working more with raster images because they are easier to manipulate, and can record data of photos with more accuracy than vector can, capturing subtle shifts in hues and values. Some popular raster file types you are sure to come across are JPG, GIF, BMP, TIFF and PNG.
Common Raster Editing Applications:
As you can see in the image above, raster images save type as squares, which can cause straight lines to look jagged or fuzzy. The vector image shows the type as flowing lines and points. It's important to note that when I make the raster image larger, the pixels become larger and the text looks worse. Raster images, though they can easily be made smaller, cannot be enlarged without losing quality. This is because the computer recognizes that it must fill a certain amount of empty space so it borrows data from neighboring pixels to fill it. This results in the image looking very blocky or "pixelated". However, when the vector image is enlarged, there isn't any distortion. You can make a vector image as large or as small as you like without ever losing the integrity of the image. They are very easy to edit since each object in the image can be selected and treated individually. Some popular vector file types are AI, SVG, FH, EPS, and WMF.
Common Vector Editing Applications:
Presently, with the exception of Scalable Vector Graphics, one cannot host a vector file within an HTML page. Luckily, you can easily convert a vector image to raster so that it may be used on the Web using the same programs you use for editing. You will be prompted to specify the size of your image and the resolution during the rasterizing process. If the image is to be printed, your raster image should have a resolution of aproximately 300 dpi (dots per inch) so that the human eye cannot see the pixels on the page. If the image is intended for the Web, 72 dpi is plenty large enough since most monitors display at 72 dpi.
While vector images can easily be converted to raster, it is not so easy to convert raster images to vector. There are some programs on the market now that claim they can, however they don't always produce the best results. Technology is always changing for the better though, so if you are interested in this process, you might want to take a look at these applications:
File size, compatibility and most importantly aesthetics should always be considered whenever you are trying to decide which file format you should go with. Take into consideration what the end product is intended for and you can't go wrong. In part 2, we'll discuss ways to compress your digital image files and I'll talk about the differences between lossy and lossless image formats. If you have any suggestions or links to similar programs of interest, I'd love to discuss them with you! Visit the forums by clicking Discuss This Article below.